The Cause of Its Own Essence
Demonstration is syllogism that proves the cause, i.e. the reasoned fact, and it is rather the commensurate universal than the particular which is causative (as may be shown thus: that which possesses an attribute through its own essential nature is itself the cause of the inherence, and the commensurate universal is primary; hence the commensurate universal is the cause).
To know its essential nature is the same as to know the cause of a thing’s existence. Some things have a cause distinct from themselves, others have not. On the one hand, essential natures which do not have a cause distinct from themselves are immediate, that is, basic premisses that must be assumed or revealed in some other way. This too is the actual procedure of the arithmetician, who assumes both the nature and the existence of unit. On the other hand, it is possible to exhibit through demonstration the essential nature of things which have a ‘middle’, i.e. a cause of their substantial being other than that being itself, but we do not and cannot demonstrate it.
Universal vs Particular
The more demonstration becomes particular the more it sinks into an indeterminate manifold, while universal demonstration tends to the simple and determinate. But objects so far as they are an indeterminate manifold are unintelligible, so far as they are determinate, intelligible. If we have a grasp of the commensurate universal, the prior, we have a kind of knowledge-a potential grasp-of the particular, the posterior, as well.
Scientific knowledge is not possible through the act of perception, for perception must be of a particular, whereas scientific knowledge involves the recognition of the commensurate universal.
Fewer Premisses the Better
We may assume the superiority ceteris paribus of the demonstration which derives from fewer postulates or hypotheses-in short from fewer premisses; for, given that all these are equally well known, where they are fewer knowledge will be more speedily acquired, and that is a desideratum.